If you have Macintosh filesystem image of an 800k boot disk, but your physical Mac has a 1.44M SuperDrive, how can you produce a physical disk that can boot that Mac?
Here's what I've been able to determine: A short filesystem on a floppy should work fine, as long as the blocks are in the right order. If the image you're using is a raw image (819200 bytes exactly, often used by emulators, that's easy. Just
fdformat the floppy device for 1.44MiB as you would for any other DOS/Windows/Linux machine and write the image using a command like,
dd bs=512 if=floppy_image.img of=/dev/floppy
However, if the image you are using comes from Apple, it will not be raw. It will be either a Disk Copy image (819284 bytes) or a
.sea self-extracting disk image, possibly with a BinHex (
.bin) wrapper. We'll address that first since it's far more common.
If the image is wrapped in BinHex, we can use The Unarchiver's
lsar to unpack the file. Note, you'd be wise to use
lsar on the file first as Macintosh files contain characters like spaces rather commonly and
unar does not provide an option to rename the output file during extraction.
At this point I recommend renaming or copying the
.sea file to one ending in the
.dmg extension and running
truncate -s 819284 your_image.dmg to produce a Disk Copy image.
Now to convert that to a raw image, you can use
dd to trim off the Disk Copy header:
dd bs=84 skip=1 if=disk_image.dmg of=disk_image.img
This leaves you with a raw disk image suitable for use with emulators or writing to a floppy as above. Note, any 800k image written to a floppy this way wastes space on the floppy disk, and the disk requires a 1.44M "SuperDrive" (a name Apple has reused time and again, but in this context refers to machines able to support the 1.44M floppy and equipped with such a drive.) Similar tricks can be used for Apple // ProDOS and GS/OS disk images if the machine is equipped with a SuperDrive and controller or other PC-compatible 1.44MB drive.
There may be other common disk formats I am not aware of for the early Macintosh. Hopefully they can be added to this answer if someone comes across one.
To create boot disks for a apple 512k macintosh I had to take a 1.44MB floppy, tape the hole to make it into a 720KB floppy, and then format the floppy as an APPLE floppy and not a PC floppy with a superdrive equipped old world g3 mac tower running osx 10.3. Then I could write the image.
A linux install on an oldworld machine with a superdrive may work to write the image IF there is a way to set the drive to 800KB mode instead of 720KB mode. For slightly newer macs, it looks like you can actually boot from a floppy with a 1.44MB format just by skipping some blocks. http://www.macfaq.org/software/macos.shtml#Q1.1.5
Real Mac/IIgs 800k floppy disks cannot be written from Linux because Apple used GCR to get 800k on the disk instead of the 720k that the PC did. You need a Superdrive to write Mac/IIgs format 800k disks.
However as @Mark pointed out you can write 800k disk images to 1440k disks from a PC and a Mac with a Superdrive will read/boot them since the disk images are bits and not sectors. Mac GUI has 800k and 1440k floppy disk images for System 6 and System 7.